The history of all internal combustion engines (e.g., Otto cycle, Diesel, and two-stroke) can be traced to 1678 when a Frenchman named Abbe Hautefeuille proposed using the power of gun powder in a cylinder to move a piston ad obtain work. His principle is used today on aircraft carriers to thrust planes into the air. The first successful working engines used walking beams, (Street's engine 1794) and rack and gear arrangements (Barsanti's and Mateucci's 1856 and Otto's and Langen's 1866) to convert the piston's reciprocal motion into rotary motion. The steam engine was the most popular source of mechanical power those days and it was not long before the crankshaft of the steam engine became a standard feature of the internal combustion engine. The crankshaft worked very well on a steam engine. The pistons seldom reciprocated more than a few hundred strokes per minute, well below destructive frequencies. The oily steam provided cooling and lubrication. The pistons were aligned so that there was no side pressure, only thrust, on the bores. The pressure was slow and steady and was often applied to both sides of the piston. Compare to this environment inside the modern internal combustion engine. The pressure is not slow but explosive. The heat is high enough to melt many metals. The working fluid is not oily steam that lubricates but white hot flames containing caustic acids. The hot gas blows by the piston and turns the oil into an etching solution.
In light of this one must admit that the modern internal combustion engines have been made very durable. However, while they may be regarded as highly developed, they are in fact less efficient than is possible since conversion of the heat energy to mechanical energy is done through the piston, connecting rod and crankshaft.
The piston's linear movement in the power stroke is the initial conversion step from heat energy to mechanical energy. The linear motion is in turn converted to the angular motion of the connection rod which in turn develops the circular motion of the crankshaft. Piston scuffing, at this stage in the conversion is caused by tremendous side pressure the crank's geometry exerts on the piston. Nevertheless, this is only one of many problems created by the use of a crankshaft.
A substantial amount of energy, and therefore efficiency, is lost from the combustion process because of the inefficiencies of the leverage geometry that is inherent in the crankshaft system. But perhaps the worst design flaw of crankshaft engines are their inherent imbalance.
A relative state of dynamic balance is achieved with the addition of compensating weights or rotating balance shafts. As engine speeds change, the resonance frequency of these weights are reached and they start to shake the engine. This creates frustrating problems for engine designers. In some modern engines as many as nine rotating and counter rotating shafts are needed to smooth this inherent imbalance.
But besides the balance problems caused by the moving mass, there is the explosive nature of the combustion process itself. An Otto cycle engine has a power generation stroke of approximately 160 degrees duration which occurs only once every other rotation (720 degrees) on a given cylinder. This translates into power input only 22% of the time. Because the pressure decreases as the volume of the combustion increases and because the leverage on the piston is changing with rotation of:the crank the forces are not transmitted in a smooth thrust as in a steam engine. This infrequent and uneven pulse of power is another inherent design problem to these engines. To overcome this, designers have pursued two routes. First, they used heavy flywheels to lessen the jolt of the explosion and carry the momentum to the next power stroke. These engines were very heavy for their power output. Some early one horse engines weighed more than a horse. Later designs were developed that use several pistons, each with their own offset on the crankshaft. This permitted the power strokes to overlap. An eight cylinder engine has four overlapping power strokes, per revolution. But this brought with it more balance problems to be overcome and more rotating and counter rotating weighted shafts and the gears or chains to power them. Any excess dynamic weight which must be designed into an engine to defeat this inherent balance flaw only adds to the inertial and friction load that the engine must overcome. These friction losses in the crankshaft system are well recognized and have been extensively studied over the years.
The combustion process in the standard Otto cycle engine is another area where improvement could be made. As far back as 1873, Brayton, an American, developed an engine which had the unique feature of utilizing the power of the complete expansion of the gases of combustion, much like the multi-stage steam engines that made ocean-going ships practical. He did this with the use of two cylinders beside each other and a very complex system of valves. One cylinder was used to pre-compress the air/fuel mixture. The other was large enough to obtain the complete expansion to atmospheric pressure of the exploded gases. Though large numbers of the engine were made the friction and inefficiency of the crank and large and complicated valve train brought only a slight improvement over the competing Otto cycle engine. Although the Brayton process was abandoned for the piston engine, it is still Used for the gas-turbine engine process.
In the last fifty years the crankshaft engine's many shortcomings has fueled a great deal of research into alternative designs. The results have brought forth several rotary designs, the turbine, and other types of compact power units. For one reason or another most have failed to capture the attention of the world's engine makers to date. There is, however, a great need, especially in the automotive industry, to develop a better engine. Initially the search was for high specific power output per pound of weight. More recently the development has focused on improved mileage and reduced pollution.
However, there are several fundamental reason why the automotive industry has not leaped into the production of any of these new engine designs. Most new engine designs lead to larger, heavier, more complex and more expensive units than conventional power plants. Also, all recent new designs have been radical departures from known, proven technology. This is particularly true of external combustion engines. But when considering the immediate, reasonable alternatives such as the Wankel rotary or the gas turbine, it is clear that each has difficulties. Both have not been widely accepted because of their poor efficiency. Another problem they share is the fact that these design cannot be easily manufactured with the billions of dollars of machine tools, special equipment and labor force that are place in the world's auto plants. Tax laws and depreciation schedules make it hard for a manufacturing firm to make a rapid change. So while these two engines' place in aircraft and small sports cars production is perhaps assured, it is not likely that the will ever be used in large numbers.
As previously noted, the conventional internal combustion engine inefficiency transfers energy from reciprocating pistons to the drive shaft because of energy losses sustained in the crankshaft connecting rod mechanism. This layout increases the complexity of the engine by requiring considerable balancing devices. Further, the conventional internal combustion engine cannot decompress the products of combustion all the way down to atmospheric pressure, thus wasting large percentages of the power potential of the combustion. Also, the conventional internal combustion engine suffers from blow-by problems (the leakage of combustion gases goes directly into the crankcase area contributing to pollution), does not burn fuel completely, creating high fuel consumption, horsepower losses and pollution emissions.
As stated above, prior internal combustion engines, including radial engines, have suffered great inefficiencies because they inadequately dealt with all the forces which are applied to the piston and connecting rod. Prior art engines, while utilizing the forces which act parallel to the centerline of the piston, have inadequately dealt with the forces acting upon the piston and rod which do not act parallel to this centerline. These extraneous forces, such as those on a crank rod when the rod is not lying along the centerline of the combustion chamber bore, are typically transferred to the piston or rod. When transmitted to the piston, the piston binds against the walls of the combustion chamber. When transmitted to a rod which passes through a bushing, the rod tends to bind. In either case, the extraneous forces lower the efficiency of the engine as the frictional forces increase on the piston and/or rod.
Therefore, an improved internal combustion engine is desirable, which would: (a) effectively control and dissipate extraneous forces from the piston and rod, (b) convert more of the energy of the expansion of the combustion gases into power output, (c) provide for the efficient conversion of reciprocal motion to rotary motion (d) reduce pollution emissions (e) be inherently dynamically balanced (f) have a large number of power pulses per revolution for smooth running, (g) provide a simple design to minimize component parts, (h) be easy to construct with the existing infrastructure found in most plants today.
Among the prior art references considered to be f interest are U.S. Pat. Nos. 3,482,554 (N. Marthins), 3,948,230 (A. Burns) and 4,334,506 (A. Albert).
U.S. Pat. No. 3,482,554 to Marthins discloses a V-type combustion engine having a lobed cam disc 3 with equally spaced cams 4. A piston rod 9 is firmly fastened to a piston 8 at one end and a roller 10 at the other. Rotation of the cam disc 3 results in upward movement of the pistons 8 and downward movement is caused by combustion thrust in the cylinder.
U.S. Pat. No. 3,948,230 to Burns discloses a rotary engine comprising a first triangular, shaped rotor 14 with clover shaped secondary rotors 15 rotatably mounted on each of three lobes 16 of the first rotor 14. The secondary rotor 15 moves in the reverse direction with each lobe engaging the concave section 29 of the base of every third piston 19.
U.S. Pat. No. 4,334,506 to Albert discloses a reciprocating rotary engine having a hollow stationary block with elliptical shaped cam surface 62. Pistons 28 are joined by piston rod 30 to a roller bearing 42. The elliptical surface allows the piston to make a complete stroke within a predetermined number of degrees of rotation in a single revolution.
The foregoing patents, however, do not disclose an improved internal combustion engine which provides for the efficient conversion of reciprocal motion to rotary motion while reducing pollution emissions and providing a simple design which minimizes component parts. Both Marthins and Albert do not disclose an engine having pistons in a radial cylinder layout. Also, those patent invention do not eliminate all unburned exhaust emissions.